The present invention relates generally to the production of bent glass sheets and, more particularly, to an improved method of and apparatus for bending glass sheets to relatively sharp angles.
Bent sheets of glass are commonly used as glazing closures in vehicles and the like. The shapes of these glazing closures may vary widely and various techniques have been developed to bend them into increasingly complex shapes of curved configurations. Sometimes, however, it may be desirable to provide a generally vertically extending sharp bend in a windshield, a backlight or a sun roof in continuation of a bead or molding strip on the surface of the hood, deck lid or roof panel. Or, it may be desirable to form two or more sharp bends in either vertical or horizontal directions to effect wrap around of a windshield or backlight into the side surface of the roof line of the vehicle. Generally, the previously accepted conventional gravity sag and press bending techniques, which have admirably served their purposes in bending glass sheets to various complex and compound curvatures, have not lent themselves satisfactorily to the production of glass sheets having sharp, angular bends therein.
One sophisticated gravity sag technique successfully developed to produce sharply bent glass is provided by the glass bending methods disclosed and claimed in U.S. Pat. Nos. 3,762,903 and 3,762,904, assigned to the same assignee as the present invention, whereby an electrically conducting path is formed on at least one surface of the glass sheet along the line about which it is desired to sharply bend the sheet. The sheet is then supported on a suitable gravity mold structure and heated in a furnace to a temperature corresponding to the softening point of the glass, causing it to sag by gravity into conformance with the shaping surfaces of the mold while simultaneously passing an electric current through said path to heat the area of the glass sheet immediately adjacent said path to a temperature above the aforementioned softening point, causing said sheet to bend along said path to form the desired relatively sharp angle therein.
While the above-described, specially modified, gravity sag method has been successful, attempts to impart sharp bends to glass sheets by previously accepted press or mold bending procedures have not been successful because it is virtually impossible to heat the glass sheet to the elevated temperatures necessary for forming the sharp bends without introducing unacceptable distortion therein.